Monolayer and Bilayer Graphene on Ru(0001): Layer-Specific and Moiré-Site-Dependent Phonon Excitations

Abstract

Graphene phonons are excited by the local injection of electrons and holes from the tip of a scanning tunneling microscope. Despite the strong graphene–Ru(0001) hybridization, monolayer graphene unexpectedly exhibits pronounced phonon signatures in inelastic electron tunneling spectroscopy. Spatially resolved spectroscopy reveals that the strength of the phonon signal depends on the site of the moiré lattice with a substantial red-shift of phonon energies compared to those of free graphene. Bilayer graphene gives rise to more pronounced spectral signatures of vibrational quanta with energies nearly matching the free graphene phonon energies. Spectroscopy data of bilayer graphene indicate moreover the presence of a Dirac cone plasmon excitation.

On-surface chemical dynamics of monolayer, bilayer, and many-layered graphene surfaces probed with supersonic beam scattering and STM imaging

“…[37][38][39][40] We will conclude this paper with ndings on the preferential adsorption of O( 3 P) on monolayer versus bilayer graphene on Ru(0001). Bilayer graphene recovers an electronic structure similar to that of free-standing graphene, [41][42][43] so side-by-side in situ comparison of the atomic products of O( 3 P) scattered on mono-and bilayer graphene provides a window into the spin-forbidden reaction dynamics of O( 3 P) on graphitic surfaces. 1 Results further show changes in the site-specicity of oxygen binding on the 3 nm graphene-ruthenium moiré pattern upon the introduction of a second graphene sheet.…”

“…While monolayer graphene experiences strong electronic coupling to the underlying ruthenium substrate, the top sheet of bilayer graphene on Ru(0001) has an electronic structure more similar to that of freestanding graphene regaining the characteristic Dirac cones of isolated graphene. 41,43 The 3 nm moiré pattern seen on bilayer graphene arises from lattice mismatch between the bottom graphene sheet and the underlying Ru(0001). The stacking of the two graphene sheets alternates between AA and AB over a larger 21.5 nm moiré pattern which arises from a 1.2% stretching of the bottom graphene layer in comparison to the more free-standing top layer.…”